No Hot Water Supply Woes and Repair T@B 400

On our last camping trip (uCamp) we had no hot water. Cold water would run through the spigots for about 10 seconds while set to hot and then stop, both on pump and city water. My first thought was the mixing valve. Before spending the money, I asked the Truma Service Rep during the first Alde session. He definitively said it couldn't be the mixing valve and that I must have the Nautilus valves set wrong.
I verified my valve setting at the site and looked in the Alde compartment. I noted the cold-water supply line to the pump was collapsed.


Reading through No Hot Water type discussions on the forum I learned of potential suction problems with cold supply check valve being installed backwards, etc. So, I assumed my collapsed line was the problem and waited until returning home to remedy things. At the house I had trouble breaking the crimp connectors on the PEX in the confined area, so I removed the assembly at the nearest screw on fittings, at the Nautilus and water pump.

With the crimp connectors and vinyl tube removed I made a new supply harness using PEX instead of the vinyl tubing. I had to trial fit several times and after it all 'dry fit' well enough I put most of the assembly together in the garage. I had to make one final connection in the T@B. All total I used two 90degree fittings and about 2feet of 1/2" PEX.

My cold-water supply through the pump is dramatically improved. It did not solve my hot-water supply issue though.
When disconnected at the mixing valve hot water flowed readily from the heater to the point where the push fitting connection enters the mixing valve. With nothing to lose, I decided to take apart the mixing valve to determine the problem. Behind the screen on the hot-water inlet side is a check valve. The screen was clear, but the valve didn't really move when gently prodded with a screwdriver. I disassembled the cold-water supply side, and the check valve moved freely. I went back to the hot-water check valve and exercised the valve, slowly increasing pressure with each push. Soon enough, it was functioning similar to the cold-water side check valve. 
Everything has been reassembled. The hot water is supply is functioning properly at all the spigots. I do not know the cause of the collapsed line or the stuck valve but am content since the system is nominal.